1. Field of the Invention
The present invention relates to a switch apparatus, a switchable power amplification apparatus which are suitable for application to a mobile telephone, a PHS phone (Personal Handyphone System), a PDA apparatus (Personal Digital Assistant) provided with a communication function, and a terminal apparatus such as a note-type personal computer using a communication function, and a mobile communication terminal apparatus.
2. Description of Related Art
Now, in Japan, the number of subscribers using mobile phones has exceeded 70% of the population, and approximately 40% of them are owners of mobile communication terminal apparatus which uses a CDMA (Code Division Multiple Access) technology. In the future, when the demand for these terminals is replaced from PDC (Personal Digital Cellular) terminal apparatus and the like by a mobile communication terminal system based on a W-CDMA (Wideband-CDMA) method, the demand for the mobile communication terminal system is anticipated to grow further.
In a mobile radio communication system using the PDC, CDMA methods or the like, such communication is secured between a mobile terminal and a base station by establishing a radio channel therebetween. However, because of a changing communication distance from the base station or due to fading in a transmission path, a signal level will change from time to time. Therefore, in a transmission system of the mobile terminal, it is arranged such that after adjusting a transmission signal to a desired signal level in a power amplifier, the signal is transmitted to the base station.
Conventionally, it has been attempted to improve an efficiency of its operation by use of a DC-DC converter in a power supply of the power amplifier in the transmission system. However, because the DC-DC converter generates a noise, and in addition, large capacity coils are required, there are many problems still to be solved.
Here, in a patent document 1 (Japanese Laid-Open Patent H9-284170), on the premise for use of an antenna duplexer, an antenna switch is disclosed which has improved a distortion characteristic of the switch by use of a grounded-gate FET as a switching element on the side of the transmitter.
Patent Document 1: Japanese Laid-Open Patent No. H9-284170.
However, according to the antenna switch disclosed in this patent document 1, because of an insufficient isolation on the side of its transmitter, there occurs a problem that a power leakage or invasion from its receiver side to its transmitter side cannot be prevented adequately, thereby making it unsuitable to be applied to handling bidirectional signals.
In the case of a switching device for outputting a plurality of signals by selectively switching therebetween, there occurs a problem that an output of one line invades another line. If this phenomenon takes place, because that an output from one line is shunted to pass to its output terminal as well as to another line, there occurs a loss in the output thereof.
A recent mobile phone is added with many functions of a so-called application such as a present location detection function with a GPS (Global Positioning System) sensor, a TV signal receiving function, an infrared communication function, a TV telephone function with a camera and the like. Therefore, an occasion of performing a high speed communication with the base station is increasing, and also a period of time for performing this high speed communication is prolonging. Thereby, an average transmission power is increasing to more than 10 mW, and thus it is required more and more to enable to deliver a transmission power which is amplified to a large power without causing any loss.
The present invention has been contemplated in consideration of the above-mentioned problems, and is configured to provide a switch apparatus, a switchable power amplification apparatus and a mobile communication terminal apparatus which are capable of preventing the occurrence of a problem of an output intrusion from one line to another line, when selectively outputting a signal from a plurality of lines, so as to be able to output the signal without a loss.